Photoelectric reading system



July 2, 1940- R. E. R. CONSTANT 2,206,527

PHOTOELECTRIC READING SYSTEM Filed March 14, 1939 f f' fn lV 'u Hg# l 7' f' f" 'Il a i a l l a 'an fL-w'f"'m w' Foser Emile Raphal Condomil'NvEN-rofe Patented July V2, 1940 UNITED STATES PATENT OFFICE PHOTOELECTRIO READING SYSTEM France Application March 14, 1939, Serial No. 261,704 In Luxemburg March 24, 1938 4 Claims.

'Ihe present invention relates to photoelectric reading systems of all kinds and, more especially to phototelegraphic systems.

It is known that in any system of transmission 5 through telephone circuits, use is made of a frequency intended to carry the signals which it is desired to transmit.

'I'he modulation of this carrier frequency by the signals produces, on either side of this carrier lo frequency, a lateral modulation band.

If n designates the pulsation of the carrier frequency and w the pulsation of the signals to be transmitted, the spectrum of the frequencies that are created is constituted:

l5 1. By the frequency the pulsation of which is il:

2. By the frequencies the pulsations of which are il-w and iH-w.

In the particular case of photo-telegraphy, it

m is possible to have all the values `ranging from zero to a maximum value wmax. which depends upon the speed of scanning of the document; therefore there is a continuous spectrum of frequencies ranging from il-wmax. to Sl-i-wmax.

It is obvious that, in order to reproduce, at the receiving station, an image as correct as possible, the above spectrum should be transmitted with a distortion as low as possible by the circuit which connects the transmitter with the receiver.

As will be readily understood, for a given circuit, the distortion becomes less, and therefore the image received becomes more correct, as the width of the spectrum Zwmax. grows smaller.

But, in this case, the speed of transmission will u be small and the time of transmission of an image will be considerable.

vIn order to obviate this drawback, the solution considered consists in transmitting between the emitting station and the receiving station a single modulation band, which is either n-w or fH-w.

These well known general principles being kept in mind, the object of the present invention is to provide a system which permits of obtaining the result mentioned in the preceding paragraph (transmission of a single modulation band) in a better manner than it was possible in prior systems.

w In most of the transmission systems of the type above mentioned, the two lateral bands are first produced, and then one of said bands is eliminated by filtering at"the emitting station.

However a filter produces, for frequencies close u to its limits, important phase distortions, which must necessarily be remedied by means of suitable compensators.

It isone object of the present invention to provide a photoelectric transmitter which produces a frequency spectrum having only one '5 lateral band.

Other objects of the invention will appear from the following detailed description.

Preferred embodiments of the presentinvention will be hereinafter described, with refer- '10 ence to the accompanying drawing, given merely by way of example, and in which:

Fig. 1 is a diagrammatical view of a system according to the present invention;

Fig. 2 is a developed view of elements of this 15 system;

Fig. 3 is a diagram of the frequency spectrum;

Fig. 4 is a diagrammatical view of a modification.

In the usual manner, the document to be trans- 20 mitted` is wound on a cylinder A. It is illuminated at a point P by lamp L and light condenser C, as shown by Fig. `1.

A micro-objective C' gives an image of the scanned point P on diaphragm O, after the light 25 beam has been cut off by a disc D provided with slots F, F', F", etc., said disc being driven by motor M.

In Fig. 2 I have shown the developement of disc D, with its slots F, F', F", and diaphragm 90 O, the whole being shown on an enlarged scale.

The-outline of diaphragm 0 is defined by the axis of the abcissa and, in the direction of the ordinates by a portion of a sinusoid.

A single slot or window is located opposite 86 diaphragm O, and there is always one slot in this position.

The interval between 2 slots is therefore equal to d, which is the length of the base of the diaphragm.

According to the present invention thedisc D is rotated in such manner that the image of thepoint P of the document on O and slots F, F', F" move either in the same direction or in opposite directions, but, in any case parallel to one another. I will show that, in this case, the spectrum of the frequencies thus created includes only the carrier frequency produced by the windows F, F', F", etc., of the disc D and only one of the lateral modulation bands, i. e., the lower 50 band, if the displacements of the image and the` slot are in the same direction, and the upperband in the other case.

As a matter of fact, the quickest modulation is producedby a sudden-passage from black to Il white or from white to black in which the separation between black and white is on a generatrix of cylinder A.

If I designate by ea the maximum width of slots F, F', F", etc., and consider the case. in which the image ofthe line of separation between a black and a white is located along line X Y, and if this line moves in the same direction as window F', the amount of light s flowing through diaphragm O and striking the photoelectric cell located on the rear is proportional to the area of the rectangle the width of which is e and the height sin nt.

s-;[1+.in su] (1) n being the pulsation of the passage of slots F, F',

F", etc.

But e is a function of the time, since the relase tive position of XY with respect to window F" varies as a function of the time.

e is of the following form:

In order to determine 1p, I consider that when the time t is zero, 1 is equal to lo, that is to say that line XY just reaches at this time the edge of the window.

Therefore BlltV 156111131 to lila.

'r being the period of pumanon of n, of rrequency F.

v is equal to t being the period of pulsation of u, of frequency f, u being the maximum pulsation of modulation created by the image.

The time necessary for the extinction of the window is:

In order to obtain the value of a informula it suffices to remark that, after a time to 1 is equal to zero.

abwesend becomes 'Iherefore, Formula 2 "=[1+ sin (mwusgn and Formula 1 becomes If now width en is equal to From this last formula results the spectrum of frequencies represented by Fig. 3, which includes: j

a. The carrier frequency;

b. 'I'helower lateral modulation band;

c. The harmonic 2 of thecarrier frequency, with its lower lateral band;

d. The low band created by the image.

It lwill be seen that it is easy, by suitably choosing n, to separate by filtering the three bands A, B, C (Fig. 3) in such manner as to utilize band B only for transmission.

Anyway, a single lateral band of modulation of the carrier n appears, and in the example that is chosen, it is the'lower band (xl-w).

Itis clear that if, instead of giving the slots of the disc and the edges of the image parallel movements in the same direction, they were given parallel movements in the opposite direction, band (1H-w) would appear.

To sum up, it is possible, at will, to cause either the lower band or the upper band to appear, but only one of these two bands and not both simultaneously.

Fig. 4 shows another modification of the de- .vice according to the present invention.

second disc D' provided with slots F, F', etc.

The image of the document to be transmitted is formed on disc D and slots F, F', etc. move at the same speed as this image.

As for disc D, it rotates at a speed which is slightly higher and serves to create the carrier frequency.

Of course, this arrangement, or others based upon the principle of the invention, might be associated with devices of known kinds, and in particular as described in the French Patent No. 804,189, of July 12, 1935.

- In a general manner, while I have, in the above description, disclosed what I deem to be practical and eiilcient embodiments of the present invention it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing Afrom the principle of the present invention as comprehended within the scope of the appended claims.

What I claim is:

1. A device for photoelectric transmission and especially telephotography, comprising, in combination, means for forming a light beam and scanning the element to be transmitted with said light beam, a diaphragm, means for projecting said light beam onto said diaphragm, a rotating disc adapted to intercept said light beam on its way to said diaphragm, said disc being provided with slots for the intermittent passage of said light beam, said diaphragm having an outline in the form of one halt of a sinusoid with a base of a length equal to the distance between two consecutive slots of said disc, and means to rotate said disc so as to move its slots in a direction parallel to that of the movement of the images of successive points oi the element to be transmitted on said diaphragm.

2. A device for photoelectric transmission, and especially telephotography, comprising in combination, means for forming a light beam and scanning the element to be transmitted with said light beam, a diaphragm, means for projecting said light beam onto said diaphragm, a rotating disc adapted to intercept said light beam on its way to said diaphragm, said disc being provided with slots for the intermittent passage of said light beam, said diaphragm having an outline in the form of one half of a slnusoid with a base of a length equal to the distance between two consecutive slots of said disc, and means to rotate said disc so as to move its slots in the same direction as and parallel to the images of the successive points of the element to be transmitted on said diaphragm.

3. A device for photoelectric transmission and especially telephotography, comprising in combination, means for forming a light beam and scanning the element to be transmitted with said light beam, a diaphragm, means for projecting said iight beam ontosaid diaphragm, two rotating discs located in front of said diaphragm, one of said discs being provided with circular holes to intercept said light beam periodically, the second disc being provided with radial slots spaced from one another a distance equal to that between successive holes in said rst disc and adapted to pass the images of the successive points of the element to be transmitted, said diaphragm being of rectangular shape with one side of the rectangle equal to the distance between two successive s1ots` of said second disc,

said discs being positioned and rotated at slightly di'erent speeds in such a manner that the frequency spectrum obtained includes only one lateral modulation band.

4. A device according to claim 3, in which said second disc is rotated at a speed corresponding to the linear speed of displacement of the images of the successive points of the element to be transmitted.

ROGER EMILE RAPHAL CONSTANT. 

